1. Field of the Invention
The present invention relates to a data transmission apparatus, system and method, and an image processing apparatus, and more particularly, to a data transmission apparatus, system and method and an image processing apparatus in a case where an image providing device such as a digital camera is directly connected, via a serial interface based on, e.g., the IEEE 1394 standards, to an image processing device such as a printer.
2. Description of Related Art
Various types of systems which transfer data to a printer via a bus are known. For example, a known technique is to output data from a computer to the printer by using a defacto standard interface such as a SCSI (Small Computer System Interface) or Centronics interface.
In other words, the printer is connected to a personal computer (PC) as a host device via a parallel or serial interface such as a centronics or RS232C interface.
Further, a digital device as an image providing device such as a scanner, a digital still camera and a digital video camera, is also connected to the PC. Image data inputted by the respective digital devices are temporarily stored in a hard disk or the like on the PC, then processed by an application software program or the like on the PC and converted into print data for the printer, and transferred via the above interface to the printer.
In the above system, the PC has driver software programs respectively for controlling the digital devices and the printer. The image data outputted from the digital devices is held as data of format which can be easily handled and displayed on the PC, by these driver software programs. The stored data is converted to the print data by an image processing method in consideration of image characteristics of input devices and image characteristics of output devices.
Today it is possible to for a new interface such as an interface based on the IEEE 1394 standards (hereinafter referred to as "1394 serial bus") to directly connect an image providing device and a printer. In case of directly connecting the image providing device to the printer by the 1394 serial bus, an FCP (Function Control Protocol) operand may include print data. Further, in the 1394 serial bus, a register area may be provided such that data transfer is performed by writing data into the register area.
Further, as the 1394 serial bus has a plurality of data-transfer control procedures, data transfer can be performed in methods appropriate to the respective devices.
Further, a printer having an image scanner function can perform printing and image scanning by selecting one of printer and scanner functions. In printing, the printer receives print data from an image providing device, while in scanning, sends image data, as an image providing device, to a host computer. That is, this printer changes a data transfer direction in accordance with its selected function.
The printer having the above image scanner function must handle bi-directional data transfer, i.e., reception and transmission of image data. For this purpose, the printer has two data transfer methods and bi-directional data transfer function. In such device, how to change the data transfer direction is important.